Clinical studies in patients with valvular heart disease and with congenital heart disease suggest that a "myocardial factor" related to dysfunction of the heart muscle itself is responsible for unsatisfactory postoperative clinical courses in certain patients. Additionally, controversies exist whether to perform palliative operations or anatomically corrective operations upon patients with congenital heart anomalies. The proper timing of operations is questioned as well. No information is available concerning the time courses of morphological changes of myocardial hypertrophy in humans and the relationships of morphological changes to postoperative clinical results. Over the previous eight years we have compared light and electron microscopic observations with clinical courses of patients undergoing operations for congenital heart anomalies associated with right ventricular systolic pressure overload. We have published descriptions of myocardial morphological alterations of right ventricular hypertrophy and degeneration in these patients during previous years. During the past year we have summarized those observations and have included additional patients under morphological and long-term clinical follow-up study.